1. Field of the Invention
The present invention relates to an organic electroluminescence unit which functions as each pixel of an active matrix display panel.
2. Description of the Related Art
Currently, the development of matrix displays using a display panel comprised of light emitting elements arranged in the shape of matrix is widely under progress. A light emitting element for use in such a display panel is, for example, an electroluminescence element which uses an organic material as a light emitting layer (hereinafter, referred to as organic EL element). Known as matrix display panel using this organic EL element are a simple matrix display panel and an active matrix display panel. The active matrix display panel is advantageous over the simple matrix display panel in lower power consumption, less crosstalk between pixels, and the like, and is particularly suitable for a large screen display and a high definition display.
FIG. 1 is a diagram illustrating the configuration of such an active matrix display panel.
As illustrated in FIG. 1, the display panel is formed with an anode power supply bus line 16 to which a power supply potential Vc for driving the display panel is applied, and a cathode power supply bus line 17 to which a ground potential GND is applied. The display panel is further formed on one surface thereof with scanning line (metal electrodes) A1-An functioning as n horizontal scanning lines, and m data lines B1-Bm intersecting each of the cathode lines. Organic EL units E1,1-En,m functioning as pixels are formed at intersections of these scanning lines A1-An and data lines B1-Bm.
FIG. 2 is a diagram illustrating an exemplary circuit configuration of an organic EL unit E formed at an intersection of one scanning line A and a data line B.
In FIG. 2, the scanning line A is connected to a gate G of an EFT (Field Effect Transistor) 10 for selecting a scanning line, and the data line B is connected to a drain D of the FET 10. The FET 10 has a source S connected to a gate G of an FET 20 as a light emission driving transistor. The FET 20 has a source S to which a power supply potential Vc is applied through an anode power supply bus line 16, and a capacitor 30 is connected between the gate G and source S of the FET 20. Further, an anode terminal of an organic EL element 50 is connected to a drain of the FET 20. A ground potential GNP is applied to a cathode terminal of the organic EL element 50 through a cathode power supply bus line 17.
Next, description will be made on the operation performed by a light emission driving control circuit (not shown) to drive the organic EL unit E.
First, the light emission driving control circuit alternately applies a scanning pulse sequentially to each of scanning lines A1-An of a display panel. Further, the light emission driving control circuit generates each of pixel data pulses DP1-DPm based on an input video signal for each horizontal scanning line, in synchronism with the timing at which each scanning pulse is applied, and applies data lines B1-Bm with the generated pixel data pulses DP1-DPm. In this event, each of organic EL units E connected to the scanning line A to which the scanning pulse is applied is to be written with pixel data, later described (hereinafter called the scanning selecting state). The EFT 10 of the organic EL unit E in the scanning selecting state turns on in response to the scanning pulse to apply a voltage based on a pixel data pulse DP supplied through the data line B to the gate G of the FET 20 and the capacitor 30, respectively. In response to the voltage applied based on the pixel data pulse DP, the FET 20 turns on to supply a light emission start current based on the power supply potential Vc to the organic EL element 50. The organic EL element 50 emits light in response to the light emission start current. Meanwhile, the capacitor 30 is charged in accordance with the voltage which is applied based on the pixel data pulse DP. The charging operation causes the capacitor 30 to hold a voltage in accordance with the pixel data to perform so-called pixel data writing.
When released from the scanning selecting state, the FET 10 turns off to stop supplying the pixel data pulse DP to the gate G of the FET 20. However, a voltage by the voltage held by the capacitor 30 is continuously applied to the gate G of the FET 20 as mentioned above, so that the FET 20 maintains its on state to continuously supply the light emission start current to the organic EL element 50. In other words, even after the release from the scanning selecting state, the organic EL element 50 continues to emit light.
In this manner, the organic EL unit E functioning each pixel of an active matrix display panel is formed with a transistor for selecting a scanning line (FET 10), a transistor for driving light emission (FET 20), and the capacitor 30 for holding pixel data, in addition to the organic EL element 50 as a light emitting element.
At present, for manufacturing a display panel having the organic EL units E arranged in a matrix form as illustrated in FIG. 1, a TFT (Thin Film Transistor) manufacturing process is used for each of the FETs 10, 20 and capacitor 30. On the other hand, an organic EL manufacturing process is used for manufacturing the organic EL elements 50.
Thus, since the process for manufacturing the FET 10 and 20 is completely different from the process for manufacturing the organic EL elements 50, the overall manufacturing process becomes complicated. In this event, it is contemplated to implement the FETs 10 and 20 with transistors using organic materials. However, the electron mobility of organic materials is lower than a silicon semiconductor, so that if the FET 20 for driving light emission is implemented by an organic transistor, the resulting FET fails to provide a driving current which causes the organic EL element to emit light at a sufficient luminance.
The present invention has been made to solve the foregoing problems, and it is an object of the invention to provide an active matrix organic electroluminescence unit which is easy to manufacture.
An active matrix organic electroluminescence unit according to a first aspect of the present invention is an organic electroluminescence unit functioning as a pixel of a display panel, which comprises an electrode panel; an organic material layer formed on the surface of the electrode panel; a dielectric layer formed near the organic material layer on the surface of the electrode panel; a metal electrode formed continuous to the surfaces of the organic material layer and the dielectric layer, and having a portion corresponding to the organic material layer functioning as a control electrode; and an organic electroluminescence element formed on the organic material layer.
An active matrix organic electroluminescence unit according to a second aspect of the present invention is an organic electroluminescence unit which is formed at each of intersections of a plurality of scanning lines and a plurality of data lines intersecting each of the scanning lines on a display panel. The organic electroluminescence unit comprises an insulating film for covering a first gate electrode extending from the scanning line along the data line near each of the intersections, and formed with the data line and a first metal electrode on a surface thereof; a first organic material layer for covering each of the data line, the first metal electrode and the insulating film; an electrode panel; a second organic material layer formed on a surface of the electrode panel; a second metal electrode formed continuous to be in contact with each of the second organic material layer and the first metal, and having a portion corresponding to the second organic material layer functioning as a second gate electrode; and an organic electroluminescence element formed on the organic material layer.